1. Technical Field
The present invention generally relates to high power interface units for robotic tool changing systems. More particularly, the present invention relates to replaceable high power electrical contacts for robotic tool changing systems.
2. Background Information
Over the past several decades, reliance on robot technology has increased significantly. While at one time the highest concentration of robot use was in the areas of electronic machinery manufacturing and automobile manufacturing, the application of robot technology now includes other diverse areas such as nuclear power generation, offshore development, disaster prevention, and other areas in which remote-controlled robot systems perform their functions quickly and accurately under difficult or dangerous conditions. More specifically, robots are now used for such diverse functions as finishing concrete, painting tall buildings, and even performing medical care. The economic and social role of robots is likely to continue to expand in the future, as advancements in robot technology make possible wider commercial application and greater improvements in industrial productivity and product quality.
Notwithstanding the expansion to other fields, robot technology remains significant in industrial applications, such as automotive manufacturing. For instance, robots continue to play a major role in automotive spot welding applications. In spot welding applications, a portable spot welding gun is installed on or attached to a robot, which is then programmed to position the gun to the desired location and produce spot welds automatically, without the need for an operator. Robots spot weld with uniformity of spot location and weld integrity.
Robotic tool changing systems permit a robot to perform various different tasks. For instance, a robotic tool changing system may enable a single robot to perform spot welding, palletize heavy loads, and engage in rigorous metal removal operations. The tool changing system allows for automatic exchange of tools as required for different jobs. A robotic tool changing system is made up primarily of two assemblies, a robot adaptor and a tooling adaptor. The robot adaptor is connected to the robot while the tooling adaptor is connected to the tool. When they are coupled together, the robot adaptor and tooling adaptor form the mechanical connection and signal interface (electrical, pneumatic, etc.), which permits the robot to perform a particular task.
Robotic tool changing systems incorporate high power electrical interface units for the transfer of high electrical energy needed for certain applications. These electrical interface units may be integral with the robot and tooling adaptor units, or they may be removably attached to the adaptor units. Robotic spot welding is one example of a robotic application which requires the transfer of high electrical power. Usage of high power electrical interface units permits the flow of high power needed for applications such as arc welding; resistance welding applications, including spot welding (both transgun and remote transformer operations), aluminum resistance welding, and stud welding; and various resistance heating applications. High power requirements typically exceed 10,000 Watts, and the following chart summarizes power requirements for some specific applications:
______________________________________ VOLTAGE AMPERAGE POWER APPLICATION (V) (i) (KW) ______________________________________ Arc Welding 80 V 150 i 12 KW Transgun Spot Weld- 460 100-200 46-92 ing Remote Transformer 460 26,000 11,960 Spot Welding Stud Welding 460 200-300 92-138 Aluminum Resistance 680 800 544 Welding Resistance Heating 110-460 10-1,000 1.1-4.6 ______________________________________
In order to achieve the high power electrical transfer for a high power robotic application such as spot welding, high power electrical contacts are integrated into the high power electrical interface units. Typically, each interface unit contains multiple electrical contacts extending into openings within an electrically insulating housing. During operation, the high power electrical interface units of the robot and tooling adapters are mated together so that their sets of contacts align and abut. Since the electrical contacts are electrically and mechanically contiguous with a heavy duty electrical cable, the transfer of high power may be realized.
Although the high power electrical contacts in the robot and tooling adapters are protected by a housing, they have a limited life cycle. Under circumstances where there is no contamination of the contacts, an average life cycle of an electrical contact is about one million cycles. The contact must then be replaced. During normal usage, however, the high power electrical contacts are subject to a number of environmental contaminants, which may drastically shorten their life cycle. For example, the high power electrical contacts may be exposed to dirt, dust, grease, water and other foreign contaminants. In spot welding operations, the high power electrical contacts are also subject to welding slag. Welding slag is molten metal that is created in the spot welding process. In the molten state, welding slag may bond to the high power electrical contacts contained in the multi-contact electrically insulating housing. In this situation, the welding slag may then solidify or become welded onto the high power electrical contacts. The molten welding slag may also solidify in mid-air, thereafter landing on the high power electrical contacts in a hardened state.
When the robot adaptor and tooling adaptor are mated so that electrical contact is made, the welding slag contamination on the contacts may cause the electrical contacts to arc, pit and/or corrode. More specifically, once welding slag adheres to an electrical contact and the contaminated contact is mated to another contact, all the current passing through the contact connection tends to divert through the hardened and attached welding slag. When such a concentration of high power occurs across the welding slag, the electrical contact may arc and become pitted. This pitting and arcing, in turn, may generate an electrical short across the mated electrical contacts.
Once an electrical contact becomes contaminated and damaged, the contact must be replaced. Presently, replacement of a contaminated electrical contact involves disassembly of the entire high power electrical interface unit and disconnection of the electrical cables, removal and replacement of the whole high power electrical contact assembly, cable re-connection and unit reassembly. Replacement, therefore, is a time-consuming, labor intensive, tedious and expensive process. Due to the labor intensive nature of replacement, there is the further possibility that the interface units and/or electrical contacts will become damaged by human error.
Thus, a need exists for an interface unit of a robotic tool changing system which provides simple and easy replacement of high power electrical contacts thereof, without the difficulty of disassembly and re-assembly of the interface units which house the contacts.